Brahms' Op. 39 is a set of short waltzes that bridge the gap between Schubertian intimacy and sophisticated piano texture. They are prized for their harmonic warmth and deeply introspective character.
Achieving a fluid, dance-like waltz rhythm while balancing the melodic voicing in the inner parts is essential.
Comparable difficulty and character — good candidates for what to learn next.
16 Waltzes (Op.39) is rated Henle level 6 of 9 — advanced repertoire, roughly ABRSM grades 7–8. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 6 — meaning you can already play level 5–6 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of 16 Waltzes (Op.39) lasts about 18 minutes.
16 Waltzes (Op.39) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Intermezzo in A major, No. 2 by Johannes Brahms, Rhapsody in G minor, No. 2 by Johannes Brahms, Liebestraum No. 3 in A-flat major by Franz Liszt — see the full similar-pieces list on this page.